(1) Technical Field
The present invention relates to a document transport device and an image forming apparatus.
(2) Related Art
An image forming apparatus, such as a copying machine, includes, for example, a document transport device called an ADF (Auto Document Feeder). The document transport device transports a document placed on a document tray to a position where image reading is performed by a CCD (Charge Coupled Device), and transports it at a speed at which the CCD can read the image at the image reading position. When the reading of the image is ended, the document is discharged to a paper discharge tray.
Recently, there is a case where a document transport device is prepared as an option device mountable to an image forming apparatus body. Although an image formation speed (that is, the number of record sheets on which images are formed per unit time) of an image forming apparatus varies according to the type thereof, when the image forming apparatus operates at an image formation speed not higher than a document transport speed (that is, the number of documents transported per unit time) of a document transport device, the document transport device can be mounted. However, in the case where an image forming apparatus having a low image formation speed is mounted with a document transport device having a document transport speed higher than that, since the document transport device transports a document at the high document transport speed as compared with the image formation speed, the so-called over-specification occurs, and there are problems that a noise generated from the document transport device becomes large, and a component of the document transport device readily reaches the end of its life.